Effect of Ca dopant on magnetic and magnetodielectric properties of Y3Fe5O12

Highlights: • Ca²⁺ doping in YIG ceramics results in the nonmonotonic variation of its saturation magnetization. • Intrinsic MD effect are observed at room temperature and its value decreases with the increase of Ca²⁺ doping. • The decrease of Fe²⁺-Fe³⁺ dipoles results in the gradually decrease and ultimate vanishing of the MD effect. -- Abstract: A series of Ca-doped yttrium iron garnet ceramics (Y_3-xCa_xFe₅O₁₂ (x = 0, 0.05, 0.1, 0.15, 0.2)) were prepared by the solid state method. The structure, morphology, valence fluctuation, thermal analysis, magnetization, magnetodielectric and Mössbauer spectrum of Y_3-xCa_xFe₅O₁₂ ceramics were systematically studied. All of the samples crystalized as single phase of garnet structure with the grain sizes of 2–3 μm. The temperature dependent percentage weight loss and heat flow were investigated by thermogravimetric (TG) and differential scanning caborimetry (DSC). The structure of Y_3-xCa_xFe₅O₁₂ ceramics was studied by XRD, Raman and Infrared (IR) spectra. The results indicated that Ca²⁺ substitution leads to lattice expansion and presence of Ca–O octahedron, which causes the concentration of Fe²⁺ decrease and Fe⁴⁺ increase. As a result, the saturation magnetization first increases and then decreases with the increase of Ca concentration. A six lines asymmetry of magnetic components were observed in Mössbauer spectrum, which was fitted by two hyperfine magnetic sextets corresponding to tetrahedral and octahedral sites, respectively. With the increase of Ca concentration, the intrinsic magnetodielectric (MD) effect disappears completely due to the dramatic decrease of Fe²⁺-Fe³⁺ dipoles. Fe³⁺-Fe⁴⁺ dipoles do not contribute to the MD properties of Y_3-xCa_xFe₅O₁₂ ceramics due to the lack of the defects such as electrons or holes being used as media.